that episode has some wierd animation. ifyou go watch "up a tree" you note several anomalities such as finn the fridge and funky physics.
giff related, it's fridgefinn. (it is even worse at other times

the art style has some consistencies that they never deviate from though.
one of the storyboarders posted several pages from their guidebook for the artstyle. most of it was be creative, but adhere to a few ground rules, that may be broken if it benefits the show visualy, such as having a somewhat clearly defined elbow, or finns shorts being formfitting and not loose, how noodle arms/legs shouldn't extend beyond the limbs, that finns face should probably never be centered in his hat, but slightly offset to create depth/space and a bunch of other stuff.